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Surface Tension in Solids and its Effect on the Mechanics of Contact and Fracture
Elasto-capillarity phenomena – solid deformation driven by liquid surface tension – have been extensively studied, but are distinct from phenomena driven by solid surface tension. The characteristic length scale that describes the deformation of a solid due to surface tension is given by the ratio between the surface tension and elastic modulus. For stiff solids such as metals and ceramics, this length is smaller than inter-atomic distances. However, for soft materials such as elastomers and gels with elastic moduli ranging from tens of Pa to several MPa, it ranges from tens of nm to hundreds of microns. Effects of this large value can be seen in different contexts. In this talk I will give several examples of how surface tension can act as a significant and even dominant agent in the mechanics of compliant materials such as elastomers and gels. In the first example, I illustrate how surface tension constraints the faithful reproduction of soft surfaces in replica molding. In the second example, I will show evidence that the adhesion of small hard particles (spheres or cylinders) on soft elastic substrates can be affected by surface tension. In the last example, I propose a theory where fracture of soft materials can be resisted by surface tension. Time permitting, I will highlight some of our recent experimental work on the measurement of solid surface tension.